Microsatellite instability (MSI) can be characterized by increased mutational load in repetitive DNA tracts (e.g., resulting from impaired DNA mismatch repair, leading to increased predisposition to mutation, etc.), such as repeated sequences of DNA (e.g., repeating units of 1-6 bp each). MSI has been shown as an indicator of treatment response, as a diagnostic phenotype in colorectal, endometrial and gastrointestinal cancers, and is recognized as an important pan-cancer biomarker. For example, MSI-high (MSI-H) has been shown as an indicator for pembrolizumab in advanced solid tumors.